As of now, Installing the apks to the /system directory seems to be working using adb push command.
Some hidden service was automatically remounting the /system directory in read-only mode.
Any way I was able to install the Play store in a normal virtual-machine ( Ie, non-Google-Api virtual machine ) by simply mounting the system.img file from my OS and by copying over the files.
# To be executed as root user in your Unix based OS
mkdir sys_temp
mount $SDK_HOME/system-images/android-23/default/x86/system.img sys_temp -o loop
cp Phonesky.apk GmsCore.apk GoogleLoginService.apk GoogleServicesFramework.apk ./sys_temp/priv-app/
umount sys_temp
rmdir sys_temp
The APK files can be pulled from any real Android device running Google Apps by using adb pull command
[ To get the exact path of the apks, we can use command
pm list packages -f inside the adb shell ]